Séminaire

One of the cornerstones of inflationary cosmology is that the large
scale structure of the Universe has a quantum mechanical origin. This
invites the question of whether compelling observational evidence for
the quantum nature of the origin can be found. Primordial
gravitational waves are generated directly from quantum fluctuations
during inflation. Since they interact with matter very weakly, travel
through the Universe virtually unimpeded, it is expected that they
keep their nonclassicality until today. In this talk, I will present

The coefficients of the operators of an effective field theory (EFT) are constrained to satisfy certain inequalities, under the (mild) assumption that the UV completion satisfies general requirements of causality and unitarity. We begin the extension of these ideas to theories where the Lorentz symmetry is spontaneously broken, as it happens in cosmology and condensed matter physics. Constraints are derived using dispersive arguments for the 2-point function of conserved currents and of the stress-energy tensor.

We will talk about a scenario that inflaton dissipates energy into another field due to an instability. The fluctuations of the new field are the dominant contribution to the primordial power spectrum and non-Gaussianities. 
 

All black holes in the Universe are believed to be rotating. This poses interesting questions, since rotating black hole solutions of Einstein’s equations of General Relativity possess a so-called Cauchy horizon in their interior, which threatens the predictability of Einstein’s theory. However, these exact solutions may not model sufficiently accurately black holes in Nature, which have classical matter in their neighbourhood and, furthermore, are inevitably surrounded by a quantum vacuum (which is responsible for Hawking radiation).

Title:  Properties of average distances and emergent causality

Abstract: In the presence of a (quantum or classical) statistical ensemble of metrics one can consider averages of distances between points/events, as long as a prescription is assigned for identifying such points. 

The spectrum of positrons in cosmic rays is currently measured with unprecedented precision by AMS-02 up to TeV energies, and represents an unique probe for the local properties of our Galaxy. Currently, its interpretation is still debated, especially for the excess above 10 GeV which suggests the presence of a local, primary source.
Recently, the observation of extended gamma-ray halos around Galactic pulsars has opened a new window to constrain the acceleration and propagation of positrons in our Galaxy.

In 2034 the Laser Interferometer Space Antenna (LISA) will detect the coalescence of massive black hole binaries (MBHBs) from 10^5 to 10^7 solar mass up to z~10. The gravitational wave (GWs) signal is expected to be accompanied by a powerful electromagnetic (EM) counterpart, from radio to X-ray, generated by the gas accreting on the binary.

In this talk I'll give recent news from workshop on Cosmic Rays and Neutrinos which was organised in APC and UCLouvain. I'll show several new experimental and theoretical results presented at this workshop 
 from the fields of  high energy neutrinos, gamma-ray astronomy and cosmic rays.
 

Two aspects of Positive Operator Valued Measures (POVM) on the Euclidean plane (a basic Hilbert space!) are presented, namely their status as quantum observables and their role as quantizers in the integral quantization procedure. The compatibility of POVMs in the ensuing quantum formalism is discussed, and a Naimark dilation is found for the quantum operators. The relation with Toeplitz quantization is explained. Within this framework, we describe the linear polarization of the light with the use of Stokes parameters and its interaction with a polariser as a quantum measurement (Malus’ law).